Renewable energy part 2) Solar energy

Contents:

• Solar thermal energy and solar panels
• Power from photovoltaic systems
• Mini PV systems for tenants

⮩ According to experts the energy demand of the entire humankind could be supplied with 100% renewable energy sources. At least from a technical point of view this would be feasible in about 30 years without any gaps in coverage. However, political and economical factors slow down development, photovoltaic systems are still uncommon for the most part.

The energy transition is first and foremost promoted by private households that have already started investing into solar energy. Home owners are confronted with the question whether they want to use their limited roof and cladding space for photovoltaic systems, solar heat or hybrid modules.

 

Sunlight can be transformed into thermal energy for heating and hot water with a high degree of efficiency. Solar panels are mounted to roofs and open spaces to harness this energy. Usually they contain a liquid heat transfer medium that carries solar heat through piping systems into the building. Even though energy self-sufficient houses powered by solar energy do exist, they are still an exception at this point. In order to guarantee a comfortable lifestyle even at night or on cold days, several different ways of storing heat have been developed. Domestic collectors are becoming smaller, more powerful and affordable.

Seasonal reservoirs that give off heat all throughout the winter still require a lot of space and have a high purchase cost. In more recently erected buildings with proper heat insulation you can implement this technology e.g. underneath the patio. Though often the location of the property is not ideal enough to use the sun to provide 100% of the heating. A value of 40 – 50% is more realistic with an increasing tendency. The rest of the required heat is covered by CO2 neutral combustion of wood.

Thanks to their low space requirements buffer vessels can be added to an existing building later during refurbishment. This technology though is not enough to last throughout the winter in most countries, though. Luckily, solar heat can be combined with heater pumps, pellet stoves, oil and gas heater systems without any problems.

Power from photovoltaic systems

Photovoltaic cells convert sunlight into usable electric power. Yet, large solar panels on the roof or garage do not appeal to everyone. However, modern photovoltaic systems are designed in a more aesthetic way and can be integrated easier into the building’s architecture than it was the case years ago. Examples for new models on the market are glass solar shingles with a slate design. Before you finalise the purchase, make sure that an electronic rectifier is integrated into the power grid. Photovoltaic systems give off direct current that needs to be transferred into the alternating current. Oftentimes those rectifiers are already included in the system, but watch out nevertheless.
 

Your roof should be able to withstand the additional weight of the photovoltaic system. Keep in mind the long service life of the system. It might make sense to completely refurbish the roof before installing photovoltaics. The installation can be done not only on top of the house but also on the sides with solar cladding or organic photovoltaics in the form of flexible film on windows. Solar film has a thickness of less than 1mm and is clear so that you can still enjoy the daylight. The efficiency of covering photovoltaic film is 13%, transparent solar cells from chemical compounds reach a value of 7%. The foils can be applied to windows (even car roofs, boats, sails, tents, etc.) and wired to a connection box.

⮩ Generally important:

• Hours of sunshine in the area must be sufficient
• No shade caused by trees, tall buildings, etc.
• Mounting surface must be big and robust enough

Do not forget to officially register your solar power station before start of operation!
 

Storage technology

Smart storage systems provide solar energy all around-the-clock. Currently, two common energy storages are used in domestic environments: lead and lithium ion accumulators. Lithium ion batteries are widely regarded as the more sophisticated technology and are becoming more and more small and appealing in design. In some cases the store can be upgraded and are available in chic looks that will not seem too obtrusive in your living room. When purchasing the accumulator you should know how much power you consume at night (stand by of household appliances). Batteries have up to 20 years of service life.

Right now development is advancing each day, promising new technologies are researched at the moment. For example super fast charging solid-state batteries are in the planning. Solar batteries / liquid batteries (redox flow) with long service life and almost completely without toxic components are enhanced currently. Other test projects to improve night storages are also ongoing. The solar thermal plant Andasol 3 in Granada, Spain has heat stores that convert power at night, even as long as 7 hours after the sun has gone down. The annual performance is 3 x 50 megawatts. Ivanpah, the largest solar plant in the world (March 2018) in the Mojave desert in South California provides 392 megawatts through parabolic trough collectors that heat up pipes filled with oil. This thermal energy is enough for a medium-sized city. A loss-free transport of the extracted power over long distances could be done by cooling special cables (superconductors).
 

Heat and power from solar heat : hybrid models

Even the biggest mansion has a limited roof space on the side facing the sun. Thanks to hybrid technology not as much space has to be sacrificed for solar cells and collectors.

Basic photovoltaic systems transform just about 15-20% of the solar energy into electric power, a rather considerable part is lost as radiant heat. The combined solar installation overcomes the problem of photovoltaic cells needing a much cooler operational temperature than heat collectors. “Double-tracked” photovoltaic systems can be connected to a cooling device, however the latter requires energy and space for a water tank. Hybrid modules are therefore only profitable in certain circumstances, for example if you have an unusually high requirement for hot water (pool, sauna).

Power extracted from sunlight (or other regenerative technologies) can be used for heating (power-to-heat). It is also possible to transform the combustion gas methane (power-to-gas). The benefit: Gas is stored easily and existing domestic gas systems can be used for transport.

 

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